1. Field of the Invention
The present invention relates to a spark advance controller and a production machine of spark advance control logic in an internal combustion engine. More particularly, the present invention relates to a spark advance controller and a production machine of spark advance control logic, which are suitable for spark advance control in a variably controlled internal combustion engine.
2. Description of the Related Art
In an ECU (Engine Control Unit) for an electronically controlled internal combustion engine, for the purpose of control of ignition timing (spark advance), a spark advance at which torque is maximized under predicted operating conditions, i.e., an MBT (Minimum Spark Advance for Best Torque), is stored in a memory in the form of a spark advance map in which each axis represents one of an engine speed and a load.
The ECU decides an optimum spark advance by referring to the spark advance map depending on the operating conditions and the ambient environment of an internal combustion engine, which change every moment, and executes control such that a gas mixture is ignited in a cylinder by an igniter at the decided spark advance. With that control, the ignition is performed at the timing of producing maximum torque without causing knock.
The spark advance map stored in the memory of the ECU is produced in the development stage of the internal combustion engine based on optimization tests using an actual engine.
In recent years, from the viewpoints of cleaning the exhaust and reducing the fuel consumption, a variably controlled internal combustion engine has been widely employed in which operating characteristics of actuators in the internal combustion engine can be variously changed depending on the operating conditions and the ambient environment.
There have been developed various types of internal combustion engines, for example, one in which the fuel concentration in a gas mixture is reduced to perform lean combustion in a particular operating range, another in which exhaust gas is supplied to an engine combustion chamber through EGR (Exhaust Gas Recirculation), and still another which includes a variably setting valve mechanism capable of optionally changing operating characteristics of intake and exhaust valves.
Because the fuel concentration (air/fuel ratio of the gas mixture), the EGR concentration, and the operating characteristics of the intake and exhaust valves, etc. cause changes in the burning state of the gas mixture within a cylinder, the spark advance has to be properly changed depending on a combination of those control parameters.
When the known optimization tests using an actual engine are performed on the above-mentioned internal combustion engines, a problem arises in point of increasing the development term and the development cost. Another problem is that, in order to make reference to respective spark advance maps with regards to all of predicted operation conditions, data maps having a very large capacity have to be incorporated in the ECU and the memory capacity of the ECU is increased correspondingly.
Against the background described above, a spark advance controller is proposed which computes various variables, such as the mass of fuel gas (gas mixture) supplied to the engine combustion chamber and the burning velocity of the gas mixture in accordance with physical models depending on an engine speed and a load, and then computes the MBT based on the computed variables (see, e.g., Patent Reference 1: JP-A-10-30535).
Also, another spark advance controller is proposed which computes various variables, such as the internal energy of fuel gas inside a cylinder at the start of compression stroke of an internal combustion engine, the piston compression work, the energy loss through wall surfaces, and the burning velocity of the gas mixture in accordance with physical models, and then computes a knock limit based on the computed variables (see, e.g., Patent Reference 2: JP-A-2003-46758).
In those spark advance controllers, during the operation of the internal combustion engine, the MBT or the knock limit is computed in the ECU online (real time) by using a plurality of physical models that describe the burning states in the engine combustion chamber. Thus, those controllers need neither the laborious optimization tests using an actual engine, nor a large number of data maps.
Further, there is known a control unit including numerical maps for various control parameters in an ECU and controlling the internal combustion engine while referring to the numerical maps based on engine operating states, wherein the numerical maps are obtained with a numerical simulator simulating the internal combustion engine (see, e.g., Patent Document 3: JP-A-2004-100495). With such a control unit, even when a large number of numerical maps are required, those numerical maps can be produced by using the numerical simulator and therefore the optimization tests using an actual engine can be omitted.
However, processing based on a physical model needs a much larger number of processing steps than that based on a map search, and the ECU is required to have a high processing capability when the ECU executes the processing during the engine operation.
Also, even in the case of producing the numerical maps by using the numerical simulator separately provided, when the internal combustion engine includes many control parameters, the number of the numerical maps is greatly increased and a memory having a very large capacity has to be incorporated in the ECU.
Thus, although the above-described techniques can noticeably reduce the number of steps required in the optimization tests using an actual engine and is expected to cut the development cost, those techniques still have a problem from the practical point of view in greatly increasing the cost of the ECU.